The present invention relates generally to an improved rotor design for a pump for transferring fragile or aggressive fluids. Examples of fragile fluids include human or animal blood, neither of which can tolerate exposure to unusual impact and/or sheer forces. Aggressive fluids include corrosive or poisonous fluids, as well as fluids which cannot tolerate contamination, or which otherwise may destroy seals and/or bearings to reduce the lifetime and/or longevity of the pump structure. Poisonous fluids, for example, are extremely dangerous if a leak develops. More particularly, the present invention relates to a rotor design for a pump which is bearing and seal-free and wherein the rotor is dynamically balanced by a combination of hydrodynamic and buoyant forces. The pump of the present invention is particularly adapted for transferring human blood and is capable of creating a flow of such liquids without damaging and/or otherwise adversely affecting the quality of the material being pumped. The rotor employed in the pump of the present invention is rotated electromagnetically by means of an electromagnetic drive system operating in conjunction with an array of permanent magnets disposed on the rotor in a brushless motor configuration. Alternatively, a permanent magnet-to-permanent magnet coupling may be employed. As such, the arrangement of the present invention is capable of achieving relative rotation while at the same time being bearing and seal-free.
In the past, pumps and pumping systems have been designed utilizing rotors which have been characterized as being bearing and seal-free. Such systems typically employ magnetic levitation means which is in effect an actual form of bearing, much the same as sleeve bearings, ball bearings, or other friction-inducing bearings. Such arrangements using magnetic bearings, while being operational and functional, may be rendered complex and accordingly require significant number of additional components including magnetic devices, position sensors, and rapid-response magnetic drive means. A number of such patents have been granted in the past, including those to Olsen et al. U.S. Pat. Nos. 4,688,998 and 5,195,877. The apparatus of the present invention, by contrast, is fully bearing and seal-free, and is provided with a rotor having a central internal bore to accommodate fluid flow input, as well as externally-positioned annular channels for accommodating flow through the pump structure. The rotor of the present invention is further designed so as to function with dynamic balance being achieved through a combination of hydrodynamic and buoyant forces.
Among the disadvantages inherent in pumps utilizing friction-reducing bearings include local heat generation such as may occur from the use of ball bearings, friction bearings, sleeve bearings, and the like. Low flow and high pressure may result in local areas due to the use of such structures. In addition, with all such bearing-equipped pumps, a high spring constant is provided wherein a small displacement of the rotor (or impeller) introduces very high forces which can damage or effectively destroy bearings. In addition, different forces are introduced in the structure whenever variations in axial positions occur.
In the present structure, the pump is bearing and seal-free, with the structure including a rotor having an internal bore for accommodating inlet fluid, and is further provided with a series of external shrouds providing multiple annular flow channels, with this design allowing for relatively high displacement without the creation of large forces otherwise required to hold a rotor in its predetermined position. The internal bore formed within the rotor is arranged coaxially with the rotor and thus fluid flow is readily accomplished therewithin. In addition, the rotor seeks and finds an equilibrium position which in certain situations can be off-set from the housing axis (in either the rotational or transverse axes) which typically occurs when the rotational axis of the pump is altered. Rotational movement of the pump housing will be manifested in displacement of the rotational or vertical axis of the rotor. The present arrangement has been found to eliminate the need for a highly precise axis in design, fabrication and operation. The lack of a positionally fixed rotational axis reduces the introduction of large forces which otherwise would be created when the axis of the rotor is shifted away from its normal centrally disposed position.
In the arrangement of the present invention, the pump includes a pumping chamber with a central axis, and with a rotor body being disposed within the chamber for bearing and seal-free rotation therewithin. The rotor has a core with a double or dual-conical configuration converging toward opposed polar regions, and with the axis of rotation extending between these polar regions. A fluid inlet port is arranged in the pumping chamber with a bore coaxially with the axis of rotation of the rotor in order to provide for inlet flow to opposed ends of the rotor. In this arrangement, the housing inlet flow is divided into two approximately equal flow portions, with the first flow portion entering the rotor at the end adjacent the housing inlet or the external inlet, and the second flow portion being drawn through the bore to the housing end opposite to the external inlet where the second flow portion makes a smooth reversal of direction and enters the rotor at the opposed end. Accordingly, one portion of the flow of fluid is transported or transferred to the portion of the rotor which is in opposed polar relationship to the housing inlet port, in other words, the external inlet. Except for those occasions when the rotor is displaced, it is normally arranged in coaxial relationship with both the pumping chamber and the fluid inlet ports. The outlet port or ports are arranged generally medially of the chamber, midway between the ends of the rotor and typically are positioned tangentially of the medial portion of the rotor and the pumping chamber. In those situations where the axis of rotation of the rotor is arranged vertically, the modified dual-conical configuration is such that flow through the bore of the rotor proceeds downwardly on the bore portion, and downwardly or upwardly on the portions external to the dual-cone shaped core.
The present rotor provides for an internal transfer of fluids between the oppositely disposed fluid inlet areas with the rotor bore forming a fluid transfer line which introduces the fluids to the rotor at opposite ends of the housing. The bore provides communication between opposite ends of the rotor, thereby permitting transfer of fluids internally of the structure, with all of the fluid being initially introduced into one polar region of the housing. The fluid is thereafter transferred internally to the oppositely disposed polar region.
The pump shown in the drawings is in operational mode with the rotor spinning about its axis of rotation and with all forces acting on the rotor balanced. In the stationary/non-operational mode with the fluid in the housing, only the buoyant forces are acting on the rotor and the rotor floats up in the random position. In the stationary/non-operational mode with no fluid in the housing, the rotor is resting on the interior of the housing under gravitational forces.
Levitation of the rotor, as indicated, is achieved by a combination of hydrodynamic and buoyant forces. Briefly, the buoyant component is achieved as a result of careful selection of the rotor density, with the preferred relative density being between about 0.1 and 0.9 of the relative density of the fluid being pumped. In a dynamic and operational mode, the buoyant forces merely become a component of lesser or secondary importance to the more significant and more highly effective hydrodynamic force.
The hydrodynamic force component is achieved as a result of the motion of the fluid as it is being moved through the pumping chamber. As the velocity of the fluid increases, the hydrodynamic forces increase substantially, and with the proper selection of rotor density, the hydrodynamic forces which are created during normal operation result in achieving a precise, steady and controllably repeatable centering of the rotor within the pumping chamber.
The pump structure of the present invention has particular application for transferring fragile and/or aggressive liquids, in particular, for transferring human blood. Since certain components in blood are extremely fragile and are damaged upon exposure to external forces, conventional pumps are simply unsuited for the application. Additionally, conventional seals and/or bearings typically found within conventional pump structures pose substantial and significant threats to cell damage. A further feature of the pump of the present invention rendering the pump well suited for transfer of blood is its essentially friction-free operation. Any frictional force creates the risk of generation of thermal energy, and thus may contribute to heat build-up. Since blood is extremely sensitive to temperature change, particularly any increase in temperature above conventional body temperature, reduction and/or virtual elimination of friction provides significant and substantial advantages.
Since the structure of the present invention does not require bearings, energy consumption is reduced through the elimination of energy losses otherwise occurring in the bearings, including energy lost in contact bearings as well as electrical losses in magnetic bearings. The driving forces for the impeller are located generally adjacent the plane of the center of gravity or center of mass of the impeller, or more particularly at least closely adjacent thereto. This feature results in the creation of a gyroscopic effect of a free-body gyroscope, and the configuration of the present invention is such as to stabilize the impeller when the axis of the housing is rotated relative to the spin axis of the rotor. In other words, the spin axis of the rotor may be altered because of a change-of-position of the housing, and thus the spin axis may not always be about the vertical axis, but can be about the horizontal axis as well. In the present arrangement, particularly as illustrated in FIG. 2, it will be noted that the magnetic drive components are offset from the transverse axis of the rotor. In this configuration, it has been found that the center of gravity or center of mass of the rotor is generally displaced from the geometric center in a direction toward the mounting point of the drive.
In addition to blood pump applications, the device of the present invention finds utility in connection with other fluids as well. Certainly non-delicate fluids may be appropriately treated and/or moved with pump devices of the present invention including the aggressive fluids as discussed hereinabove.
The elimination of shafts, bearings and seals substantially reduces the manufacturing cost of the pump of the present invention. Also, the pump of the present invention has a mechanical lifetime which is virtually unlimited under normal conditions. The device of the present invention finds utility for a variety of fluids when economy, longevity, and uninterrupted service are factors in selection and/or application.
In accordance with the present invention, only one inlet to the housing is provided, and correspondingly only one line of plumbing to the pump is required. Offsetting the plane of the drive means from the outlet/medial plane of the housing further makes the pump design, operation, and maintenance more convenient and allows one to use a conventional drive means, especially in the permanent magnet-to-permanent magnet configuration.